1. Field of the Invention
The present invention relates generally to scroll compressors which include intermeshing fixed and orbiting scroll members and, more particularly, to mechanisms for biasing the orbiting scroll towards the fixed scroll.
2. Description of the Related Art
A typical scroll compressor comprises two facing scroll members, each having an involute wrap wherein the respective wraps interfit to define a plurality of closed compression pockets. When one of the scroll members is orbited relative to the other member, the pockets decrease in volume as they travel between a radially outer suction port and a radially inner discharge port. The pockets thereby convey and compress a fluid, typically a refrigerant, contained therein.
During compressor operation, the pressure of the compressed refrigerant tends to force the scroll members axially apart. Axial separation of the scroll members causes the closed pockets to leak at the interface between the wrap tips of one scroll member and the face surface of the other scroll member. Such leakage reduces the operating efficiency of the compressor and, in extreme cases, may result in the inability of the compressor to operate.
Undesirable leakage at the tip-to-face interface between scroll members can also be caused by a tilting or wobbling motion of the orbiting scroll member. This tilting motion is the result of overturning moments generated by forces acting on the orbiting scroll which are not symmetrical about the axis of the orbiting scroll. More specifically, the drive force imparted by the crankshaft to the drive hub of the orbiting scroll is spaced axially from forces acting on the scroll wrap due to pressure, inertia and friction. The overturning moment acting on the orbiting scroll member causes it to orbit in a slightly tilted condition so that the lower surface of the plate portion of the orbiting scroll is inclined upwardly in the direction of the orbiting motion. Wobbling motion of the orbiting scroll may result from the interaction between convex mating surfaces, particularly during the initial run-in period of the compressor. For instance, the mating wrap tip surface of one scroll member and face plate of the other scroll member may respectively exhibit convex shapes due to machining variations or pressure and heat distortion during compressor operation. This creates a contact point between the scroll members, about which the orbiting scroll has a tendency to wobble until the parts wear in. The wobbling perturbation occurs in addition to the tilted orbiting motion described above.
Efforts to counteract the separating force applied to the scroll members during compressor operation, and thereby minimize the aforementioned leakage, have resulted in the development of a variety of prior art axial compliance schemes. For example, it is known to axially preload the scroll members toward each other with a force sufficient to resist the dynamic separating force. Another approach is to assure close manufacturing tolerances for component parts and have the separating force borne by a thrust bearing or surface.
Pressurized gas or liquids may also be used to resist the separation forces which develop between the fixed and orbiting scroll members. In a compressor having a pressurized, or "high side", housing, discharge pressure has been used on the back side of the orbiting scroll member to create a compliance force to oppose the separating force. It is also known to use an intermediate pressure zone behind the orbiting scroll member or a combination of discharge pressure zones and suction pressure zones disposed behind different portions of the orbiting scroll whereby the pressure zones create a net upward force to oppose the separating force. Still another axial compliance mechanism for a scroll compressor involves exposing a radially inner portion of the orbiting scroll member bottom surface to oil at discharge pressure, and a radially outer portion to refrigerant fluid at suction pressure. Compressor designs utilizing a combination of pressure zones require the use of seal means engaging the bottom surface of the orbiting scroll member to separate the respective pressure zones.
Oftentimes such seal means comprise an O-ring seal disposed in a groove located in either the rear surface of the orbiting scroll member or in the bearing pad thrust surface. When the scroll compressor is not operating the pressure zones will assume a pressure equal to that of the surrounding atmosphere and the orbiting scroll will drop down into contact with the thrust surface. The movement of the orbiting scroll member may force the O-ring seal to be disposed entirely within the groove and thereby degrade its sealing ability. When the scroll compressor is once again started, the O-ring seal will remain disposed within the groove and have a reduced sealing capacity until the high pressure zone located radially inward of the O-ring seal lifts the orbiting scroll member off of the bearing pad and the O-ring seal drops partially out of the groove to more effectively engage both the thrust surface of the bearing pad and surfaces defining the groove on the rear of the orbiting scroll member.
An axial compliance mechanism which inhibits the tilt and wobble of the orbiting scroll member and improves the performance of sealing means located between the orbiting scroll and bearing pad is desired.